DevTools: Fix zombie execution contexts in the console
DevTools: Fix zombie execution contexts in the console

When a RuntimeModel with multiple execution contexts was removed,
some of the execution contexts could be unintentionally left in the
ConsoleContextSelector.

Change-Id: I8fea191af5a2f02c1de350866d29ddffe24338f6
Reviewed-on: https://chromium-review.googlesource.com/1038794
Reviewed-by: Dmitry Gozman <0ca14b32cbb359a30ac562af27dd84cc2813eacb@chromium.org>
Commit-Queue: Joel Einbinder <bab755abe9fee48fe544272e55f73517d4e4a725@chromium.org>
Cr-Original-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#555296}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: deec77c695767d1f469c4a59153f920e5dac3033
ChromeDevTools/devtools-frontend,dart-archive/devtools-frontend,ChromeDevTools/devtools-frontend,dart-archive/devtools-frontend,ChromeDevTools/devtools-frontend,dart-archive/devtools-frontend,dart-archive/devtools-frontend,ChromeDevTools/devtools-frontend,dart-archive/devtools-frontend,ChromeDevTools/devtools-frontend,dart-archive/devtools-frontend,ChromeDevTools/devtools-frontend